The present invention relates to a system and method for performing partial cylinder cut-off of an internal combustion engine, and more particularly, to a system and method for performing partial cylinder cut-off of an internal combustion engine in which the operation of a predetermined number of cylinders is discontinued in a low load state such that fuel consumption and exhaust gases are reduced.
An internal combustion engine that is used as a power source for vehicles operates by supplying an air-fuel mixture to a combustion chamber, igniting the mixture, and using the resulting combustive force to drive a piston. In particular, the piston undergoes rectilinear motion by the applied force, and this rectilinear motion is converted into rotational motion by a crankshaft assembly.
Exhaust gases generated by the combustion of fuel are expelled from the engine into the air. The harmful substances in the exhaust gases, that is, hydrocarbons(HC), carbon monoxide (CO), and nitrogen oxides (NOx), are a major cause of air pollution. As a result, most countries have emission standards in place that must be met by automobile manufacturers. In an effort to satisfy increasingly stringent emission laws and regulations, there is continuing research to reduce the harmful exhaust gases by automobile manufacturers.
A relatively new method of reducing emissions is that of discontinuing the operation of a predetermined number of cylinders in a low load state (i.e., during idle and low speeds) such that a rotational force sufficient only to prevent the engine from stalling is provided. In addition to reducing exhaust gases, the cutting off of one or more cylinders during a low load state improves fuel efficiency. Examples of this new technique are disclosed in Korean Patent No. 2000-020351 and Korean Patent No. 1998-062253.
In Korean Patent No. 2000-020351, fuel supplied to two cylinders in a four-cylinder engine is cut off in a low load state such that the amount of exhaust gases is reduced by fifty percent. In Korean Patent No. 1998-062253, engine rpm are detected and compared with a predetermined rpm stored in an electronic control unit. If it is determined that the engine is in an idle state, the injection of fuel is discontinued for specific cylinders.
However, in the case of Korean Patent No. 2000-020351, since the valves continue to operate normally even with the discontinuation of the supply of fuel, intake air is exhausted through the exhaust system. This causes an increase in the time required to reach a catalytic activation temperature when the vehicle is first started, which acts to increase emissions. Also, because of the cooling effect of the intake air on the cylinder block, the catalytic cleansing efficiency is reduced by the mixture of ignited and un-ignited fuel. Therefore, it becomes necessary to completely re-design the exhaust system. However, the resulting structure capable of overcoming these problems is complicated and heavy.
In the case of Korean Patent No. 1998-062253, since control is performed by merely detecting engine rpm, no flexibility is provided for special conditions such as consideration for differing loads. Also, un-ignited fuel is directly exhausted through the exhaust system.
The present invention provides a system and method for performing partial cylinder cut-off of an internal combustion engine, in which the operation of a predetermined number of cylinders is discontinued in a low load state (during idling, at low speeds, etc.) such that fuel consumption and exhaust gases are reduced.
In a preferred embodiment of the invention, a system comprises a rocker arm including first and second arms that are selectively joined together; a rocker arm connecting unit for performing an operation of selectively joining the first and second arms of the rocker arm; a separation-preventing unit interposed between the rocker arm and the rocker arm connecting unit, the separation-preventing unit preventing separation of the rocker arm from the rocker arm connecting unit; and a hydraulic pressure supply unit controlled by an electronic control unit to supply and exhaust hydraulic pressure to and from the rocker arm connecting unit, the electronic control unit performing control of the hydraulic pressure supply unit according to comparisons made between received signals of vehicle state and pre-installed data.
The rocker arm connecting unit preferably comprises a support bracket including a chamber formed within the support bracket and a passageway through which hydraulic pressure is supplied to and exhausted from the chamber, the chamber including a first section and a second section, the second section having a smaller diameter than the first section; a linking shaft including a first land formed on an innermost end of the linking shaft and slidably provided in the first section of the chamber, a second land formed at a predetermined distance from the first land and slidably provided in the second section of the chamber, and an outer sleeve formed on an end of the linking shaft opposite the first land, the outer sleeve operating to selectively connect the first and second arms of the rocker arm; and a first elastic member interposed between an innermost wall of the chamber and the first land of the linking shaft.
The rocker arm may be separated into the first and second arms at substantially a center portion thereof, in which each of the arms includes a substantially circular indented portion, the first and second arms being assembled with the indented portions abutting one another, the indented portions of the first and second arms being formed to enable the first and second arms to be freely rotated within a predetermined rotational angle, the indented portions of the first and second arms include sleeve holes formed at a predetermined diameter in a center of the indented portions, and the indented portions include teeth formed protruding toward the center of the indented portions, wherein teeth are formed on an outer circumference of the outer sleeve, the teeth of the outer sleeve being selectively meshed with the teeth of the indented portions of the arms.
The first elastic member preferably is a compression spring that provides a constant biasing force to the linking shaft in a direction of the rocker arm.
The separation-preventing unit in a preferred embodiment may comprise a slide rod provided within the outer sleeve of the linking shaft; a cap coupled to an outermost end of the outer sleeve, the slide rod being slidably inserted into the cap, the cap acting as a guide for the sliding motion of the slide rod and for preventing the slide rod from exiting the outer sleeve; a second elastic member interposed between the cap and a head of the slide rod, the head being formed at an innermost end of the slide rod; and a two-stage rod including a large diameter section and a small diameter section, the two-stage rod being attached to the slide rod in a state such that the small diameter section is inserted into the sleeve hole of the second arm and the large diameter section is flush with an outer surface of the second arm, thereby preventing separation of the rocker arm from the rocker arm connecting unit.
A plurality of protrusions are preferably formed on an outer circumference of the head of the slide rod, and grooves corresponding to the protrusions are formed in an inner diameter portion of the outer sleeve such that the protrusions are able to slide within the grooves.
The hydraulic pressure supply unit preferably comprises a hydraulic pump for generating hydraulic pressure, the hydraulic pump being mounted on a line in communication with the rocker arm connecting unit; an ON/OFF solenoid valve controlled by the electronic control unit and mounted on the line downstream from the hydraulic pump, the ON/OFF solenoid valve allowing the supply or cutting off of the supply of hydraulic pressure from the hydraulic pump to the rocker arm connecting unit; a check valve mounted on the line downstream from the hydraulic pump; a reservoir mounted on the line between the check valve and the rocker arm connecting unit; and an exhaust solenoid valve provided between the check valve and the reservoir.
A method according to a preferred embodiment of the invention for performing partial cylinder cut-off of an internal combustion engine comprises determining if cut-off conditions are satisfied; and discontinuing opening and closing of intake and exhaust valves for a predetermined number of cylinders if the cut-off conditions are satisfied.
According to a further alternative embodiment, the method of the invention comprises determining if a time that a transmission is in neutral exceeds a first predetermined time; determining if a vehicle speed is 0 if the time that the transmission is in neutral exceeds the first predetermined time; discontinuing the operation of intake and exhaust valves for a first predetermined number of cylinders if the vehicle speed is 0; determining if an accelerator pedal is controlled to on in a state where the operation of the intake and exhaust valves for the first predetermined number of cylinders is discontinued, reactivating the operation of the intake and exhaust valves for the first predetermined number of cylinders if the accelerator pedal is controlled to on, and returning to discontinuing the operation of the intake and exhaust valves for the first predetermined number of cylinders if the accelerator pedal is not controlled to on; determining if the accelerator pedal is controlled to on if the time that the transmission is in neutral does not exceed the first predetermined time; determining if a time that the accelerator pedal is in an off state exceeds a second predetermined time and if a change in vehicle speed is less than 0, in the case where the accelerator pedal is not controlled to on; discontinuing operation of intake and exhaust valves for a second predetermined number of cylinders if the time that the accelerator pedal is in an off state exceeds the second predetermined time and if the change in vehicle speed is less than 0; determining if the accelerator pedal is controlled to on in a state where the operation of the intake and exhaust valve for the second predetermined number of cylinders is discontinued, and reactivating the operation of the intake and exhaust valves for the second predetermined number of cylinders if the accelerator pedal is controlled to on; and determining that the vehicle speed is 0 if the accelerator pedal is not controlled to on, returning to discontinuing the operation of the intake and exhaust valves for the first predetermined number of cylinders if the vehicle speed is 0, and returning to discontinuing the operation of the intake and exhaust valves for the second predetermined number of cylinders if the vehicle speed is not 0.